What a load of bull shark: tracking danger in canals

Busting myths about the sharks, commonly described as aggressive and with a history of local attacks, a research team are getting surprising results from a 'hands on' monitoring project.

"I like predators," says Dr Jonathan Werry, a scientist with a job description to defy fears of most mortals.

On a canal near you, standing in his small but modified boat (stabilised so not to fall on overboard) the Large Shark Research Scientist is holding a young bull shark in a harness and tank as water is pumped through his gills.

On this mission, Dr Werry's PhD thesis with Griffith University, sharks larger than 1.3 metres stay out of the boat.

"There are ways you can handle a very big shark to both of your advantage," he calmly describes.

He's been fitting tags, with 24 of the sharks getting special acoustic tags that emit a unique signal allowing the team to track shark movements between holes and around the murky waters of the Gold Coast canals and Nerang River.

Dispelling myths

Far from being attracted to canals by human activity, destruction or modification of natural waterways may be forcing the sharks into canals from their natural home in Nerang River, estuary and coastal waters.

After thousands of hours in the field, losing on average one night of sleep a week, Jonathan Werry has found that young pups prefer the low salinity of the upper river. Not till they grow and their physiology changes do they want to range further into salty environments.

"The natural 'courseway' of the river has a lot more established tidal flows and a lot more structure such as mangroves in the upper reaches, which potentially provide a better food source for these animals," describes Jonathan.

A large bull shark tracked moving around the approximately 200km length of Gold Coast canals surprised the researcher with insights into how they might modify their behaviour.

"He'd roam about during the week and then find a deep hole and settle there for the weekend when the water was busy with human activity," he says.

Murky danger

Holes are an important habitat for bull sharks making them a dangerous recreation spot for humans.

"You can't see the animal and they can't see you, although they probably know you're there."

Bull sharks are 'quite smart' and not necessarily aggressive says Dr Werry, rather more likely to bump and bite a human if the reflection of a palm resembles something like the mullet they're hunting.

"Dusk, dawn and during the night the shark's movement increases significantly.

"And a big rainfall event can drive them into new areas where they might not be expected."

There are less than one hundred roaming the canals and Nerang River in his best estimate.

But stories of shark encounters are numerous and have found their way into local lore with some substantiation after fatal attacks, most recently in 2003.

"They are very good at what they do; hunting and consuming prey," he says.

"But they still have big issues of conserving energy and maximising survival."

The sharks - Dr Werry discovered from 110,000 detected animal movements - have particular patterns of behaviour; information that can be applied to reduce risks to humans and manage health of the ecosystem.

An overpowering catch

Dr Werry's most exciting catch for this research was a large female found almost 10 km up the Nerang River.

Telltale signs of waterway health

Jonathan describes a boom and bust scenario where shark numbers are affected by habitat modification and fishing for fins.

"When you remove top predators out of an ecosystem the numbers and breeding of smaller species becomes unbalanced, resources are depleted and in time the whole system degrades.

"We're seeing females return to the same river where they were pups despite degradation.

"A question is, overtime will we see a shift away because the river can no longer sustain their young."

Tracking the big ones

Jonathan Werry couldn't wait to graduate from cleaning turtle tanks at Seaworld and start diving with the big guys.

"There's something about their mystique and people's fearful perception of them," he says.

"A lot of injuries can be related back to fear."

The scientist has had one bite - on his right foot, and plans for that to be all. If anything, it has spurred him on, driven by conservation of the species and producing meaningful, relatable information.

Away from Gold Coast waterways you might find Jonathan offshore, surgically inserting a tag into a 3 metre Tiger shark or even larger Dusky Whaler. The tag will last ten years and provide unprecedented information about shark movement up and down the east coast and into rivers.

The Queensland Large Shark Tagging program is already making interesting finds; Dr Werry tells of the tracking of two large bull sharks both tagged at Jumpin Pin, who moved from Bundaberg to Mackay to Cairns and back to Bundaberg in a four month period.

The biggest bull shark he's seen was off the south east Queensland coast.

"It was 3.2 metres long, but most impressively its girth and weight was threefold that of a 2m shark.